*2.2. Thermophysical Traits of Hybrid Nanofluid*

The physical traits of hybrid nanofluids are prescribed in Table 1. In Table 1, the subscript *hnf* , *n f* , *f* and *s* signify the hybrid nanofluid, nanofluid, fluid and nanoparticle, whereas *s*1 and *s*2 symbolize the first nanoparticle and second nanoparticle, respectively. Furthermore, *ϕ*1 represents the first nanoparticle volume fraction while *ϕ*2 denotes the second nanoparticle volume fraction. In this investigation, copper (Cu) is picked as the second nanoparticle volume fraction, alumina (Al2O3) is picked as the first nanoparticle volume fraction and water act as a base fluid. Table 2 displays the thermophysical traits of nanoparticles and base fluid. It is important to note that Al2O3 is originally disseminated into the water to achieve the appropriated hybrid nanofluid, i.e., Cu-Al2O3/water, and then Cu is disseminated into the Al2O3/water nanofluid. Additionally, the volume fraction of Al2O3 nanoparticle is set to 1% and Cu is fluctuated from 0 to 2%.

**Table 1.** Physical traits of hybrid nanofluids (Devi and Devi [38]).


**Table 2.** Thermo physical properties (Oztop and Abu-Nada [61]).

